Per the ADA read on DoD regulations:
"The Standards of Retention: Current Army Servicemembers Who
Control Diabetes without Medication Do Not Need a Medical
Evaluation; Applicants for Enlistment with Diabetes Must Get a
Waiver and Meet the Standards of Retention; and Current
Servicemembers Who Use Any Medication for Diabetes Must
Have a Medical Evaluation."

And:
"Servicemembers with diabetes mellitus will be referred to an
MEB “unless hemoglobin A1c can be maintained at < (less than) 7% using only lifestyle
modifications (diet, exercise).” Army Regulation 40-501, “Standards of Medical Fitness,”
3-11(d) (January 14, 2008). Applicants for enlistement may request and be granted a
waiver, but must still meet the standards for retention, and so these individuals must be
able to control their diabetes solely with diet and exercise and maintain an A1C of 7% or
less. Similarly, an individual already in a military position in the Army who was
diagnosed would not be referred to an MEB and would be able to remain in the Army so
long as his or her diabetes was controlled without medication with an A1C of 7% or less.
Those individuals who attempt to enlist will be subject to the diabetes ban if diagnosed
with diabetes requiring any form of medication, or who do not take medication but have
an A1C above 7%, because they will not meet the standards of retention."